Sometimes only partial images are downlinked in order to reduce
downlink data volume using a process called "windowing". The region of
interest, also called the "window", is captured from the LORRI detector
and the rest of the image is not even downlinked. However, the
subsequent ground processing populates the missing regions with zeroes
and then subtracts the bias level, which produces negative numbers in
the final calibrated image. This combination of negative numbers in the
"Blank Region" and "Real Data" in the windowed region, and the automatic
intensity scaling used to produce the JPEG image (which ranges from the
minimum to maximum values in the image), produces a banded structure in
the JPEGs. A similar effect also applies to images for which data have
been "lost" (e.g., data dropouts at the Deep Space Network).